A decoding method for decoding an encoded multichannel audio signal into the original signal has been developed. Herein, the encoded audio signals are obtained by converting the original signals into a down-mixed main signal (a stereo frequency signal), a residual signal, and spatial information and, subsequently, encoding these signals.
For example, in order to encode a surround audio signal, such as a 5.1 ch audio signal, the MPEG surround standard (ISO/IEC23003-1) defined by ISO/IEC has been used. In the MPEG surround standard, a surround signal is converted into, for example, a 2-channel main signal contained in an original audio signal, a residual signal indicating an error component generated when the audio signal is prediction-encoded, and the spatial information and, thereafter, the signals and information are encoded. In an MPEG surround decoder, the surround audio signal is obtained by decoding the main signal, the residual signal, and the spatial information.
The residual signal indicates an error component generated when the audio signal is prediction-encoded. By using the residual signal when the surround audio signal is prediction-decoded, an error occurring during prediction-encoding may be corrected. Thus, the audio signal prior to prediction-encoding may be accurately reproduced.